1. Technical Field
The present invention relates to white ink for ink jet recording and a recording apparatus involving the white ink.
2. Related Art
An ink jet recording method has been typically known, in which ink droplets are ejected from a nozzle of an ink jet recording head to form characters and images.
In recent years, a wide variety of inks have come to be used in the ink jet recording method. In the case where color images are recorded on recording media having surface color which is not white, such as plastic or metallic products, white ink containing a white pigment is selected from such a wide variety of inks to hide the surface color in some situations, which can enhance color development of the color images. In recording of color images on a transparent sheet, the white ink is used to form a white shielding layer to decrease the transparency of the color images (see JP-A-2008-248008). Hence, the white ink has been required to exhibit high whiteness after being applied onto a recording medium.
The white pigment contained in the above-mentioned white ink settles in an ink jet recording apparatus due to the difference in specific gravity between the white pigment and a solvent in some cases.
In such a case, if a sediment containing the white pigment (also referred to as a hard cake) is soft to some extent, a fluid (an ink or a cleaning solution) is allowed to flow through the interior of the ink jet recording apparatus to discharge the sediment from a nozzle of an ink jet recording head.
If the white pigment-containing sediment becomes solidified or thick, however, the sediment cannot be completely removed by the flow of a fluid through the interior of the ink jet recording apparatus in some cases. In such a circumstance, the sediment may prevent proper supply of ink or cause defective ink ejection.